1. Field of the Invention
The present invention relates to a stepping motor drive device including a plurality of insulated gate semiconductor elements (for example, power MOSFETs) that apply drive voltage in a complementary way to paired coils of a stepping motor, thus driving the stepping motor.
2. Description of the Background Art
A stepping motor 1 includes a plurality of pairs of coils 3a, 3b, 4a, and 4b provided enclosing a rotor 2, as shown in FIG. 5. FIG. 5 shows a schematic configuration of a main portion of a two-phase unipolar type of the stepping motor 1. The stepping motor 1 is excited by current being caused to flow in a complementary way to the paired coils 3a, 3b, 4a, and 4b, as shown in, for example, FIG. 6, because of which the rotor 2 is rotary driven in increments of a predetermined angle.
FIG. 7 is a schematic diagram of an overall configuration of a stepping motor drive device 10 that drives the stepping motor 1. The stepping motor drive device 10 includes parallel drive circuits 11, 12, 13, and 14 that apply drive voltages Vout1, Vout2, Vout3, and Vout4 in a complementary way to terminals Xa, Xb, Ya, and Yb of the coils 3a, 3b, 4a, and 4b. Input pulse signals Vin1, Vin2, Vin3, and Vin4 generated by a timing generator 15 and having the kinds of predetermined phase difference shown in FIG. 6 are input into the drive circuits 11, 12, 13, and 14 respectively, thus generating the drive voltages Vout1, Vout2, Vout3, and Vout4.
Further, the drive circuit 11 (12, 13, 14) includes an insulated gate semiconductor element, for example, a power MOSFET 22, that is driven on and off by a gate drive circuit 21, generates the drive voltage Vout1 (Vout2, Vout3, Vout4), and applies the drive voltage Vout1 (Vout2, Vout3, Vout4) to the coil 3a (3b, 4a, 4b), as shown in, for example, FIG. 8. Herein, the gate drive circuit 21 receives the input pulse signal, which is provided via a logic circuit 23, and generates a gate signal, thus driving the power MOSFET 22 on and off (for example, refer to JP-A-2011-239242).
Reference sign 24 in FIG. 8 is an overheat detector circuit that detects overheat trouble in the power MOSFET 22 via an unshown temperature sensor. Also, reference sign 25 is an overcurrent detector circuit that monitors the current flowing to the stepping motor (load) 1 via serially-connected resistors r1 and r2. When overheat trouble is detected by the overheat detector circuit 24, or when an overcurrent is detected by the overcurrent detector circuit 25, the logic circuit 23 drives on a protective MOSFET 26 connected to the gate of the power MOSFET 22. By the MOSFET 26 being driven on, the gate voltage of the power MOSFET 22 is compulsorily set to the ground potential, and the drive of the power MOSFET 22 is stopped. Because of this, the stepping motor (load) 1 and power MOSFET 22 are protected from the heretofore described troubles.
Also, when the drive of the power MOSFET 22 is controlled so as to stop by the logic circuit 23 in this way, information thereon is output to the exterior as a status signal ST via a MOSFET 27. Also, when a disconnection of the stepping motor 1, that is, a disconnection of the coil 3a (3b, 4a, 4b) is detected via serially-connected resistors r3 and r4, information thereon is output to the exterior as the status signal ST via a MOSFET 28 provided in parallel with the MOSFET 27.